MP3 on Wii

Hi All. I undertstand the Wii can play MP3 files. I loaded some MP3'S and photos on my SD card. I can view the photos fine. But cannot even see the MP3 files. I have searched but can't find and info. When I go to the photo channel all I see are the photos. I bought the system on 4/1 have it hooked to my broadband connection. The system did go through an update. Can anyone help?